What is it doing? When you switch off and get out of the car, you will hear the tick, tick, tick from the valve block as it self levels (same when you unload a weight out of the boot, when you close the doors the rear will drop down), but it will self level down to whatever height it is currently at. So if you stop and it is at Standard, it will level to that, if you've just come off the Motorway and it is still at Motorway height, it will level down to that. This does assume it is being parked on a flat surface or it will level down to the lowest corner. When you next get into it, it should still be at the height it was left at. If it has settled, it will show the Access light lit with the Standard height light flashing until it rises up to that.
If it is dropping to Access as soon as you get out, I would suspect an iffy height sensor reading low or the calibration bits have been input wrongly so it is levelling down to match the lowest corner.